For people with post-traumatic stress disorder (PTSD), like combat veterans or survivors of disasters, or those with crippling phobias, such as fear of heights, snakes or job interviews — the traditional treatment is exposure therapy: in the presence of a doctor, you confront the feared thing mentally or physically until you achieve “extinction” of the association between the fear and the feared thing.

To confront an exaggerated fear of bridges, for example, a patient under a therapist’s guidance might be taken repeatedly to a bridge until she could finally cross it.

In a 21st-century twist on the treatment, Dr. Difede is using virtual reality — computer-generated environments that look, sound and feel “real” — as a highly effective and often less lengthy and costly innovation in exposure therapy. She began by treating phobias, creating, for example, a virtual plane for those with fear of flying. After the World Trade Center attack, she decided to build a virtual reality environment to try to help traumatized 9/11 victims and rescue workers. At the virtual site the attack and its aftermath are recapitulated slowly, step by step. Unlike the uncontrolled situation of PTSD, in which the terrifying memory keeps recurring suddenly and unbidden, the patients using virtual reality become slowly habituated to the memory in a safe environment they can control. The success of her efforts with the 9/11 patients has led Dr. Difede to expand her disaster repertoire. She is currently working with Cornell Weill’s world-renowned burn center to develop a simulated kitchen fire, a tragically common occurrence affecting particularly old people and the very young. A Hurricane Katrina version of the program simulates an escape from a flooding apartment in a building that looks very typical of New Orleans’ French Quarter.

While still very new, virtual reality therapy has generated considerable attention. Dr. Difede, one of its earliest practitioners, is currently collaborating with colleagues at the University of Southern California, who have created a “Virtual Iraq” for combat-related PTSD. A few years ago, Dr. Difede says, there were only a couple of sites that had battle software. Now, under contract with the Department of Defense, she and her colleagues have trained over 150 military psychologists, psychiatrists and social workers, and equipment and software are being distributed across the country. The government is also funding clinical trials to compare virtual reality treatment with other treatments, including drug treatments, currently in use.